In general, a permanent-magnet synchronous motor can efficiently utilize energy and generate less heat, compared with an induction motor, and can therefore be easily subjected to weight reduction. Therefore, demands for a permanent-magnet synchronous motor have been increasing in recent years.
Such a permanent-magnet synchronous motor needs to be controlled by applying a voltage from a VVVF inverter in accordance with a rotation position of a rotor of each permanent-magnet synchronous motor. Therefore, individual control corresponding to each permanent-magnet synchronous motor is required. Accordingly, a special VVVF inverter is provided for each permanent-magnet synchronous motor, and a gate control apparatus for controlling each VVVF inverter is provided (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2004-143577).
Therefore, the number of control apparatuses increases in a conventional system which controls individually each permanent-magnet synchronous motor. Increase in size of the entire apparatus and increase in costs have caused problems. Therefore, “trolley control” of controlling a permanent-magnet synchronous motor in control units of two motors is introduced, and increase in size of the apparatus is reduced (for example, Jpn. Pat. Appln. KOKAI Publication No. 2009-72049).
FIG. 9 is a circuit diagram of an electric-vehicle control apparatus which introduces conventional trolley control. Line power is supplied to a first main circuit 200 and a second main circuit 300 through a current collector (pantograph) 100, a high-speed breaker 101, a charging-resistance shortcircuit switch 102, a charging resistor 103.
The first main circuit 200 comprises: a first opening contact device 104; a first filter reactor 105; an overvoltage limit circuit comprising a first overvoltage limit resistor 107 and a first overvoltage limit resistor switch 108; a first and a second direct voltage detector 109a, 109b; a first and a second inverter filter capacitor 110a, 110b; a VVVF inverter 111a, 111b forming a 2-in-1 inverter unit 120a. 
VVVF inverter 111a for the permanent-magnet synchronous electric motor 115a converts a power-line current as a direct current into an alternating current. The converted alternating current is supplied as a drive force to a permanent-magnet synchronous motor 115a through a current sensor 112a connected to a three-phase line, an electric-motor release contactor 113a, and an electric-motor internal voltage detector 114a. VVVF inverter 111a and VVVF inverter 111b are configured in the same manner as each other, and are connected in series with each other. The inverters form a 2-in-1 inverter unit 120a and share one heat radiator.
The second main circuit 300 is configured in the same manner as the first main circuit 200. The 2-in-1 inverter unit 120a and 2-in-1 inverter unit 120b are connected in parallel with each other. As a ground, a wheel 116 is connected to each of the 2-in-1 inverter unit 120a and the 2-in-1 inverter unit 120b. 
FIG. 10 is a block diagram showing a gate control system of an electric-vehicle control apparatus shown in FIG. 9. As shown in FIG. 10, the 2-in-1 inverter unit 120a is provided with an overvoltage-limit controller element 107 and a gate control apparatus 130 for controlling VVVF inverters 111a and 111b. The inverter unit 120b is also configured in the same manner as above. In the figure, equal numerals surrounded by circles indicate that connection is made to each other. The power supply for the gate control apparatus (common controller 131) is provided for each set of 2-in-1 inverter units 120a and 120b. 
The gate control apparatus 130 controls, by itself, VVVF inverters 111a and 111b and on/off of the overvoltage-limit control element 108. Therefore, output currents detected by current sensors CTU1, CTW1, CTU2, and CTW2 for VVVF inverters 111a and 111b, and an electric-motor internal voltage based on electric-motor internal-voltage detectors 114a and 114b are input to the gate control apparatus 130.
The output of the 2-in-1 inverter unit 120a is connected to each of the permanent magnet synchronous motors 115a and 115b. Control units depend on individual control methods. The release conductor 104 and filter reactor 105 are provided respectively for VVVF inverters 120a and 120b, and control units each are 2-in-1 inverter units for electric motors.
In a conventional electric-vehicle control apparatus for a permanent-magnet synchronous motor using a 2-in-1 inverter unit, a large number of semiconductor elements need to be equipped. For each 2-in-1 inverter unit, a filter reactor, an overvoltage limit resistor, and an overvoltage limit control resistor switch are provided. Therefore, a large number of components are used, which makes it difficult to reduce the size of the entire apparatus.
One embodiment has an object of providing an electric control apparatus capable of individually controlling a permanent-magnet synchronous motor and reducing the size of the entire apparatus.